I was transporting rifle squads in trucks and wagons, when I noticed the passenger was not being displayed on some of the vehicles, but was displayed on others. The status bar lower left indicated a passenger was onboard. It just wasn't being displayed on the map.

Edit: When I moved the vehicles, the passengers reappeared on the map.

It was an odd thing to happen. I know it appeared this way at the beginning of a turn, because all the units have 7 APs. I know the passengers were displayed in the previous turn. I believe they either disappeared after I clicked the "Next Turn" button or when I designated artillery strikes.

In the image I included with my original post, you can barely see it, but the adjacent truck on the selected unit's left and the adjacent wagon on the selected unit's right both have two sevens real close together, one for the vehicle and one for the passenger. All three of these units actually have rifle squad passengers. I had not selected these units yet this turn, so they didn't disappear from me clicking on the vehicle.

It's odd that other three trucks in the screenshot have rifle squad passengers and are displayed normally.

Maybe the passengers didn't get redrawn after a nearby Russian artillery strike or something. I don't know.